Changes in climate, land management and fire regime have contributed to woody species expansion into grasslands and savannas worldwide. In the USA, Pinus ponderosa P.&C. Lawson and Juniperus virginiana L. are expanding into semiarid grasslands of Nebraska and other regions of the Great Plains. We examined P. ponderosa and J. virginiana seedling response to soil water content, one of the most important limiting factors in semiarid grasslands, to provide insight into their success in the region. Photosynthesis, stomatal conductance, maximum photochemical efficiency of PSII, maximum carboxylation velocity, maximum rate of electron transport, stomatal limitation to photosynthesis, water potential, root‐to‐shoot ratio, and needle nitrogen content were followed under gradual soil water depletion for 40 days. J. virginiana maintained lower Ls, higher A, gs, and initial Fv/Fm, and displayed a more gradual decline in Vcmax and Jmax with increasing water deficit compared to P. ponderosa. J. virginiana also invested more in roots relative to shoots compared to P. ponderosa. Fv/Fm showed high PSII resistance to dehydration in both species. Photoinhibition was observed at ∼30% of field capacity. Soil water content was a better predictor of A and gs than Ψ, indicating that there are other growth factors controlling physiological processes under increased water stress. The two species followed different strategies to succeed in semiarid grasslands. P. ponderosa seedlings behaved like a drought‐avoidant species with strong stomatal control, while J. virginiana was more of a drought‐tolerant species, maintaining physiological activity at lower soil water content. Differences between the studied species and the ecological implications are discussed.

Vegetation in grasslands is changing at an unprecedented rate. In the Nebraska Sandhills, this shift is attributed in part to encroachment of the woody species Juniperus virginiana. We investigated changes in resource availability and their N, and N content, compared to grasslands. Water potential was higher in trees in grasslands compared to dense stand. J. virginiana in dense stand exhibited similar trends to trees in grasslands for net photosynthetic rate (P N ), stomatal conductance, transpiration, maximum photochemical efficiency of PSII, maximum carboxylation velocity, and maximum rate of electron transport. P N peaked early summer and declined in the fall, with trees in open grasslands lagging behind those in dense stand. Plasticity of this species may place it at a competitive advantage in the Sandhills, further altering grasslands vegetation and ecosystem processes.

Federally funded range improvement treatments in the United States require that land managers consider the treatment's impacts to archaeological sites. Pending archaeological clearance can result in the postponement or exclusion of effective seeding practices, which in turn can result in poor seed establishment, increased weeds, recurrent fire, accelerated soil erosion, and damage to cultural sites. Less intensive requirements would help relieve time restrictions, but less-conspicuous sites might be missed. We quantified the displacement and damage that lithic artifacts would incur if missed in an inventory and subsequently subjected to drill seeding treatments. We subjected chert, quartzite, and obsidian materials to impact by a rangeland drill and a no-till drill on sandy and silty soils. Soil texture was the most important factor in perpendicular lithic movement. In the silty soil, lithics were displaced perpendicular to the direction of the drill nearly twice as far as in the sandy soil (7.8 cm 6 0.9 SE vs. 4.1 cm 6 0.6 SE, P , 0.01). No experimental factor showed a difference in absolute displacement (mean 5 15 cm). Damage to lithics was infrequent (25%) and minor with no experimental factor showing statistical significance. Approximately 30% of lithics were buried by treatments. In the sandy soil, the rangeland drill buried lithics 6.5 mm 6 1.6 SE deep, on average, which was twice as deep as the no-till drill in the sandy soil (3.0 mm 6 0.9 SE) and four times as deep as both drills in the silty soil (1.5 mm 6 0.5 SE; P 5 0.03). Minimal effects of drill seeding on lithics suggest that drill seeding could proceed with lessintensive archaeological surveys. Resumen Los tratamientos de mejoramiento de pastizales financiados por el gobierno federal de los Estados Unidos requieren que los manejadores de la tierra tomen consideren el impacto de los tratamientos en los sitios arqueológicos. Dependiendo del permiso arqueológico puede dar lugar a demora o a la prohibición de prácticas efectivas de resiembra, que puede traer como consecuencia, pobre establecimiento de la semilla, incremento en malezas y fuegos recurrentes, erosión acelerada del fuego, y dañ o a los sitios culturales. Unos requisitos menos severos ayudarían a reducir las restricciones del tiempo, pero en sitios menos visibles esto se podría ignorar. Evaluamos el disturbio y el dañ o que los instrumentos de piedra podrían producir si se ignoraran en un inventario y posteriormente se incluyeran para llevar a cabo en los tratamientos de la siembra. Nos enfocamos en los materiales de cuarzo, obsidiana y xert al impacto de la sembradora de pastizales en suelos arenosos y arcillosos. La textura del suelo fue el factor más importante en el movimiento perpendicular lítico. En el suelo arcilloso, los líticos fueron perpendicularmente desplazados en la dirección de la sembradora casi dos veces en comparación con los suelos arenosos (7.8 cm 6 0.9 SE vs. 4.1 cm 6 0.6 SE, P , 0.01). Ningún factor experimental demostró una diferencia en la separación absoluta (media ...

No abstract